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7.0
CALIBRATION PROCEDURES AND FREQUENCY
This
SOP stipulates minimum calibration requirements necessary to ensure that the
measuring system is capable of producing acceptable data.
Acceptable calibration protocol must involve a demonstration that the
instrument or measuring system is capable of acceptable performance at the
beginning of the analysis sequence and that initial calibration is still valid
after continued system operation.
7.2.1 Calibrations must be performed
according to all analytical method directives OR as indicated in this Guidance
Document if specifics are not addressed in the cited method.
7.2.2 Analytical method calibration
acceptance criteria must be followed or if acceptance criteria are not specified
in the method, general criteria presented in this SOP shall be used to verify an
acceptable calibration.
7.2.3 The number of calibration standards used to
achieve an acceptable calibration must adhere to the cited method.
If this information is not in the method, then a minimum of a blank and 3
standards must be employed to develop calibration curves.
See Section 7.6.3 for guidance on other types of analyses.
7.2.4 At least one of the calibration standards
shall be at a concentration of 1 - 2 times the laboratory practical quantitation
limit for the method. By using a
calibration standard at that level, the laboratory can verify the PQL with each
initial calibration.
7.3
STANDARD
RECEIPT AND TRACEABILITY
7.3.1 Records to be retained for primary stock
standards must include source, type of standard, date of receipt, lot number (if
applicable), expiration date and purity statement.
7.3.2 Records to be maintained for preparation of
intermediate standards must include identification of primary standards used,
preparation date, methods of preparation (including specific dilution
information), preparer identification, concentration prepared and expiration
date.
7.3.3 Preparation records for working
standards must include identification of primary
and intermediate standards used in working standard preparation, date of
preparation, method of preparation (including dilutions), concentrations
prepared and preparer identification.
7.4
FREQUENCY
OF STANDARD PREPARATION AND STANDARD STORAGE
1.
Standards must be stored according to analytical method guidance or
supplier recommendations.
2. If no method or
supplier guidance is available standards must be replaced upon decreased
instrument response.
7.4.2
Frequency of Standard Preparation
1. If
no method or supplier guidance is available standards must be renewed upon
decreased instrument response.
2. It is recommended
that all primary standards be held for no longer than one year.
3. Working standards are
to be prepared on a daily basis unless specific method guidance stipulates
differently.
7.4.3 Tables specifying standard storage protocol
and standard preparation frequencies must be available for inspection at the
laboratory.
7.5
MINIMUM
CALIBRATION REQUIREMENTS FOR FIELD INSTRUMENTS
This section will discuss
pre-inspection calibration, field calibration, office/lab calibration, and use
of field instruments. Please note
that instrument-specific or model-specific calibration and operation procedures
are not included. If the following
procedures do not apply to your particular equipment, the pertinent analytical
reference and the manufacturer's operating/owner's manual shall be used for
specific protocols.
7.5.1.1 Calibration
of field instruments shall be performed on a regular basis with records kept on
the field sheets, field logs or in a separate calibration log.
The records must indicate the method used to calibrate, the time and
date, number of standard(s), resulting meter response, actions taken, and the
results of the calibration. Optionally,
the meter: name, model number, and identification number (if applicable) may be
entered.
7.5.1.2 Maintenance
and repair notes shall be made in the maintenance logbook for each meter.
If rental equipment is used, a log is not required.
However, the origin (i.e. rental company), rental date, equipment type,
model number and identification number (if applicable) shall be entered into the
field notes or a rental equipment notebook.
7.5.1.3 Prior
to mobilization, the Project Manager must verify that all equipment is in proper
working condition, calibrated, and that batteries are properly charged.
7.5.1.4 Field
calibration of each meter shall occur daily, at the first sample site and must
be verified throughout the day (see 7.5.1.5 below).
This will ensure field data of a known quality.
All field calibrations and checks shall be noted on field sheets.
7.5.1.5 Minimum
Quality Control Requirements
a.
The QA Rules no longer require the generation of historically derived QA
Targets of precision and accuracy for field measurements.
In lieu of taking duplicate measurements and using independent QC check
standards, more frequent continuing calibrations shall be performed.
b.
Once the meter has been calibrated, these checks shall take place at
intervals of no more than 4 hours and at the end of the sampling day. For instance: the
pH meter will be checked against the pH 7 buffer, thermistors will be checked
against field-grade thermometers, conductance meters will be checked against one
KCl standard, etc.
c.
If a field meter fails a continuing calibration, a complete initial
calibration must be performed. In
this way, meter response will be addressed without the need for generating
historical precision and accuracy statistics.
7.5.1.6
Documentation on calibration standards (e.g., buffers, KCl, and other
reagents) must be maintained.
a.
At a minimum, the date of receipt, expiration dates (noted on the bottle
label), and date of first use shall be noted on the standard container.
b.
Expiration dates must be followed.
c.
If reagents or standards are prepared from stock chemicals, they must be
analytical reagent grade or better. NOTE:
Potassium chloride standards must be of primary standard grade.
7.5.2.1
General Concerns:
a.
The pH meter is field calibrated on a daily basis at the first site.
Since field meters do bump around from site to site, calibration is
likely to change. Calibration
checks must be made per 7.5.1.5 above.
b.
Calibration may be checked on a weekly basis in the office or laboratory
to ensure the % theoretical slope is not less than 90%, indicating a bad
electrode. This should be noted in
the calibration records. If % slope
cannot be determined on your meter, or the manufacturer's optimum specifications
are different, manufacturers recommendation for maintaining optimum meter
performance shall be followed.
c.
There are several interferences to keep in mind with pH measurement:
1.
sodium at pH > or = 10 can be reduced or eliminated by using a low
sodium error electrode;
2.
coatings of oils, greases, and particulates may impair the electrode's
response. The electrode bulb should be patted dry with lint-free paper
or cloth and rinsed with deionized water. If
not, acetone may be used to clean very hard to remove films, but must be used
sparingly so the electrode surface is not damaged;
3.
temperature effects on the electometric measurement of pH are controlled
by using instruments having temperature compensation or by calibrating the meter
at the temperature of the samples;
4.
poorly buffered solutions with low specific conductance (<200
umhos/cm) may cause fluctuations in the pH readings.
Equilibrate electrode by immersing in several aliquots of sample before
taking pH.
d.
Follow the instructions with each type of pH meter. Use secondary
standard buffer solutions (pH of 4, 7, 10) purchased from commercial vendors for
calibration. Do not reuse buffers.
e.
Each meter/electrode system must be calibrated at a minimum of two
points, at least three pH units apart, bracketing the expected sample pH.
Check historical data for expected pH or use pH paper on an aliquot to
estimate.
f.
Under normal conditions a pH measurement should be accurate to +/- 0.1 pH
unit. Remember the needle of the pH
meter must align with its image on the mirror on the gauge to get an accurate
reading. Similar care must be taken
when recording digital read-out.
7.5.2.2 Calibration
and Field Use
a.
Check the battery before mobilizing and turn on the meter when you reach
the first facility and allow it to equilibrate to ambient temperature.
b.
Calibrate the meters prior to taking samples:
1.
Estimate the sample pH range (e.g., history, operator, litmus)
2.
Turn function switch to pH position
3.
Select the appropriate buffers to bracket the expected sample pH, either
pH 4 buffer and pH 7 or pH 7 and pH 10.
4.
Remove the protective cap, rinse the electrode with deionized water (DI)
and dab dry with lint-free paper or cloth.
5.
Place and swirl the electrode in the pH 7 buffer and turn the calibration
knob until the reading is 7.0. Repeat
step 4 above.
6.
Place and swirl the electrode in the second buffer solution (pH 4 or 10).
Adjust the temperature knob until the reading is that of the pH standard.
Repeat step 4 above.
7.
Measure the temperature of the second buffer solution.
8.
Turn the slope indicator until the arrow of the temperature compensator
points to the temperature of the buffer. The
percent to the theoretical slope should be read from the slope scale.
A slope of less than 90% (or one not meeting the manufacturer's
specifications) indicates a faulty electrode or contaminated buffer and the
problem should be corrected before proceeding.
c.
After calibration follow these procedures to take a pH reading of a
freshly collected sample:
1.
Pour enough fresh sample into a pH measuring cup to take a reading and
measure its temperature. If it
differs more than 2 C from the buffer temperature, adjust for the difference by
turning the slope indicator until the arrow to the temperature compensator
points to the sample's temperature.
2.
Place and swirl the pH electrode in the sample (in the cup) and read the
pH value. In the case of low
specific conductance and meter drift, add 1 ml of 1M KCl (potassium chloride)
solution to each 100 ml of sample, swirl and read pH.
Note: to make 1M KCl solution, take 74.55 grams of primary standard
grade KCl and add it to a 1 liter volumetric flask. Add DI to the 1 liter line on the flask and mix.
Solutions of the appropriate strength may be purchased from commercial
laboratory suppliers.
3.
Turn the meter off after the last reading, discard the sample in the cup,
rinse the electrode thoroughly with deionized water and replace the electrode's
rubber cap.
d.
The QAS no longer requires performing duplicate measurements (precision)
or independent check standards (accuracy).
These QC checks are optional and do provide an excellent check of
instrument response and operation. In
lieu of performing these checks, additional calibration checks will be
mandatory. Continuing calibration
must be done per the following:
1.
After the initial calibration, the pH meter shall be checked against the
pH 7 buffer at intervals of no more than 4 hours.
2.
The meter will also be checked against the 7 buffer after sampling has
been completed.
3.
If the sampling event takes less than 4 hours, then an initial
calibration and a post-calibration check will be adequate.
4.
If, during the continuing calibration, the response is greater than .2 pH
units on either side of 7, then a complete initial calibration must be
conducted.
5.
All initial and continuing calibrations shall be completely documented in
bound notebook or field sheets, including: date/time, standard(s) used,
resultant meter response, action taken, and technician initials.
7.5.3.1
General Concerns
a.
Temperature determinations can be made with any field-grade
mercury-filled, alcohol-filled, or dial-type Celsius thermometer as well as an
electronic thermistor. The dial
type thermometer is preferred over the glass type for field work because of its
durability and ease of reading.
b.
All thermometric devices shall, at a minimum, be checked annually in the
laboratory against a National Institute of Standards and Technology (NIST)
precision thermometer. If data is
generated for submission to DER as a Monthly Operating Report for domestic or
industrial wastewater, this calibration check must be increased to quarterly.
1.
The temperature measuring device should be checked at two temperatures
against the NIST precision thermometer.
2.
Temperatures should agree within +/- 0.1 C.
Make note of the calibration in the calibration records.
Note the make, model, and
serial number of each thermometer.
a.
Thermometers that do not meet the acceptance criteria should be disposed
of properly.
b.
If the difference is shown to be constant (i.e. + 0.5 C) over the
thermometer range, the thermometer may be used provided that the difference is
documented for 10 degree increments, and the correcting factor is used in all
measurements.
c.
Use care and proper cleaning procedures to prevent sample
cross-contamination.
7.5.3.2 Calibration
and Field Use
a.
All field-grade thermometers must have completed the annual check against
the NIST-grade thermometer. All
thermistors must be calibrated in the field with a field-grade (or NIST-grade)
thermometer.
b.
Allow the thermometer or thermistor (always use one which has been
properly calibrated) to equilibrate to ambient temperature.
c.
Insert thermometer or thermistor in situ when possible or in a portion of
the sample. Swirl and take readings
when the mercury column, needle, or read-out becomes constant; record the
temperature to the nearest 0.5 C. Read
to the nearest 0.1 C for a digital gage.
d.
Continuing calibration must also be performed for thermistors. The thermistor should be checked against the field-grade
thermometer at 4 hour intervals and at the end of the sampling day.
7.5.4.1 Introduction
The electrode method is predominantly used in situ for dissolved oxygen
(DO) determinations.
7.5.4.2
General Concerns
a.
Before sampling the DO meter should be calibrated in water saturated air
to make sure it is operating correctly. The
DO meter should be calibrated on samples free of interference, in the
laboratory, and against the Azide modification of the Winkler Method of
determining dissolved oxygen on an annual basis.
b.
Turbulence is necessary to keep a constant flow of water across the
membrane-sample interface. Be sure
the stirrer is working before using the probe.
c.
Store the probe with a cover that creates a saturated atmosphere.
A cap, with a wet sponge in it, will suffice.
d.
Before mobilizing, check to make sure there are no bubbles beneath the
probe membrane and no wrinkles or tears in the probe membrane. If so, replace the membrane and KCl. Check the leads, contacts, etc. for corrosion and/or shorts
if meter pointer remains off-scale, does not calibrate, or drifts.
e.
Dissolved inorganic salts are an interference with the performance of DO
probes. For example, the taking of
DO readings in salt water is affected by the salinity and must be corrected by
adjusting the salinity knob. Adjust
the meter based on readings taken from the specific conductivity/salinity meter
or use appropriate calculations to correct for salinity.
f.
Reactive gases which pass through the membrane may interfere. For example, chlorine will depolarize the cathode and cause a
high probe output. Long term
exposures to chlorine will coat the anode with the chloride of the anode metal
and eventually desensitize the probe. Sulfide
(from H2S) will undergo oxidation if high enough potential (voltage) is applied,
creating current flow, yielding faulty readings.
If such interferences are suspected, the membrane electrode should be
changed frequently, and must be calibrated at more frequent intervals.
g.
DO probes are temperature sensitive, and a method of temperature
compensation is normally provided by the manufacturer.
7.5.4.3 Calibration
and Field Use:
a.
Annual Laboratory Calibration
1.
Fill a clean bucket with uncontaminated or deionized water and place the
probe into the bucket. Siphon water from the bucket into two Biological Oxygen
Demand (BOD) bottles. Make sure to
place siphon hose on the bottom of the bottles and overflow the bottles by three
volumes. Determine the DO by the
Winkler method (see Standard Methods for the Examination of Water and Wastewater
for more details).
2. Adjust
the DO meter according to manufacturer's instructions.
Be sure to adjust the meter to the temperature of water in the bucket,
then calibrate the DO indicator dial to read the average DO concentration of the
two samples determined by the Winkler test.
3.
Keep a calibration log.
4.
If the air calibration seems to operate properly but the oxygen
concentrations disagree with the results of the Winkler calibration by more than
0.2 mg/L it is time to have the electrode or meter serviced or replaced.
b.
Prior to mobilizing and at each sample site, air calibrate the DO meter
in water saturated atmosphere to make sure the meter is reading correctly.
1.
Turn meter on for at least 10 minutes before the initial field
calibration and use. With lint-free
paper or cloth, wipe any droplets off the membrane surface.
For YSI meters, and most others, the meter must remain on redline to keep
the membrane polarized. Do not turn
off until the end of the day.
2.
Once the probe/calibration chamber are stable at ambient temperature,
check the air temperature and determine, from the DO versus temperature table
(usually on the meter's battery pack), what the DO should measure.
(You can't get a stable ambient temperature if the probe is sitting in
the sun).
3.
With the probe as close to the water surface as possible (saturated
atmosphere) turn the knob to read DO. Adjust
the calibration knob until the DO reading is at the theoretical level determined
in b.2. above.
c.
Using the salinity measurement (if appropriate) from the conductivity
meter, adjust the salinity control knob on the DO meter (ignore if your meter
automatically adjusts for salinity). Take
the DO reading and record it on the field sheet.
d.
Place the DO probe at the depth and location appropriate to what you are
measuring. For example, take the DO
of an effluent just before it enters a receiving water.
If the effluent has cascading or other aeration prior to entering the
surface water, take the DO reading in the receiving water right where it enters.
For well mixed surface waters, e.g., fast flowing streams, take the DO
reading at approximately 1-2 feet below the surface or at mid-depth.
For still or sluggish surface waters, take a reading at one foot below
the surface, one foot above the bottom, and at mid-depth.
If it is shallow, say less than two feet, take the reading at mid-depth.
Do not take a reading in frothy/aerated water since you may get a false
reading.
e.
Keep the probe in the saturated atmosphere (see 7.5.4.2.c above) between
sites and events. If the readings
show distinct, unexplainable changes in DO levels, or when the probe has been in
waters with high sulfides, recalibrate using the Winkler method.
f.
While taking a reading, if it is very low, e.g., below 1.0 ppm, allow it
to stabilize, record it and then, remove and rinse the probe, as the environment
is very likely anoxic and may contain hydrogen sulfide, which can damage the
probe.
g.
Continuing calibration must also be performed on the DO meter. The meter should be air calibrated at 4 hour intervals and at
the end of the sampling day.
7.5.5
Specific Conductivity Meter
Specific conductance is a useful method to approximate the total amount
of inorganic dissolved solids. Conventional
conductivity devices consist of two or more platinum electrodes separated by a
test solution. The major
disadvantage with this type of system is the possibility of polarization or
poisoning (fouling) of the electrodes. Conductivity
systems based on the measurement of inductance or capacitance are also
available. The electrodes in these
systems are insulated by a layer of glass or other insulating material.
System response is less rapid, but problems with fouling and polarization
are eliminated. Conductivity varies
with temperature. For example, the
conductivity of salt water increases 3%/degree C at O C, and only 2 %/degree C
increase at 25 C. Therefore, it is
necessary to record temperature with conductivity measurements or to adjust the
temperature of the samples prior to making conductivity measurements.
Most conductivity meters have temperature compensation.
7.5.5.1 General Concerns
a.
Follow the manufacturer's instructions.
b.
Samples are preferably analyzed at 25 C.
If not, temperature corrections are made and results reported at 25 C.
c.
With good equipment an accuracy of +/- 1% of the reading is achievable.
d.
Typically a conductivity meter is combined with a thermistor to measure
water temperature. The temperature
measurements are used for both conductivity and DO corrections.
7.5.5.2 Calibration and Field Use
a.
The meter should be checked in a laboratory in one of three ways:
1.
Follow method specifications;
2.
Use two standard potassium chloride solutions of 100 and 1,000 umhos/cm
or standards that bracket the range of expected sample conductance; or
3.
A single check standard in each range of a multi-range instrument.
b.
If the meter does not read within 1% of the standards, determine what the
problem is and correct it before proceeding.
Most field instruments read conductivity directly.
If the meter does not correct all values to 25 C, calculate corrective
factors using the procedure in 7.5.5.3 below.
Record all readings and calculations in the
calibration records.
c.
The meter must be calibrated in the field with at least one KCl standard
prior to analyzing the first sample. The
chosen standard must be close to the conductance value of the real samples.
d.
Use during a sampling event:
1.
Turn the meter knob to redline before use.
Follow the manufacturer's recommendations or redline approximately 15 -
20 minutes before use.
2.
When at a site or facility adjust the redline knob to align the needle
directly over the redline, using the mirror reflection, if available.
3.
Typically, the conductivity probe is immersed at the same time, depth,
and location as the DO probe. Measure
the water temperature with the conductivity probe.
4.
If the meter is equipped with automatic temperature compensation, adjust
the temperature knob on the conductivity meter to the water temperature and read
the conductivity. The conductivity meter has a set of positions which multiply
the reading by powers of ten in order to measure the full range of potential
conductivities. You will need to
set this dial to the correct range in order to take a reading.
The reading, with the temperature gauge adjusted properly, reports
conductivity measured at 25 C.
5.
Switch the dial to take a salinity reading.
Use this reading to adjust the DO meter for salinity, if necessary.
This should not be used for reporting salinity as a measured parameter,
since the calibration is not directly applicable. It may be used as an estimate for salinity for compensation
of a DO measurement.
6. If
using at more than one site or sampling location, keep the probe polarized by
turning the meter's knob to redline and keeping the probe in water between
locations.
7.
Continuing calibration must be performed on the conductance meter.
The meter should be checked against the one KCl calibration standard at 4
hour intervals and at the end of the sampling day.
8.
Rinse off the probe with deionized water and turn off when finished for
the day. Store the probe in
deionized water at all times, if it dries out it takes 12 - 24 hours to
rejuvenate it.
7.5.5.3 Calculations
a.
If the meter does not automatically correct for temperature, or if a
probe with a cell constant other than 1 is used, the following formula shall be
used to correct the data to 25 C:
K =
Km)(C)
1 + 0.0191(T-25)
Where: K
= conductivity in umhos/cm at 25 C
Km = measured conductivity in umhos/cm at T
degrees C
C =
cell constant
T =
measured temperature of the sample in degrees C
If the cell constant is 1, the formula for
determining conductivity becomes:
K =
(Km)
1 + 0.0191(T-25)
b.
Refer to SM 2510B, 17th edition, if other calculations (i.e. determining
cell constant, etc.) are required.
Residual chlorine is unstable in aqueous solutions and as such its
concentration decreases rapidly with time.
Exposure to sunlight (or other strong light) or agitation will accelerate
chlorine reduction; therefore, analysis should begin immediately after sampling.
Field colorimetric kits are available to test for the presence of
chlorine. The colorimetric method
which requires the use of a spectrophotometer (HACH DR-100) and the amperometric
method are approved by EPA. Some visual colorimetric tests using DPD chemistry and color
wheels are EPA approved for domestic wastewater sources.
The colorimetric spectrophotometer method is more desirable because of
its ability to be calibrated. The
subjective nature of assessing a titration endpoint used in the amperometric
method reduces precision. The
colorimetric method reduces human error. The
amperometric method is better to use when there are matrix interferences in the
wastewaters. For example, the
lignins in pulp and paper wastewaters could cause a background color
interference in the colorimetric method. A
complete discussion of the methods are found in Standard Methods for the
Examination of Water & Wastewater, 17th. Edition.
Organic vapor meters may be used to perform qualitative or screening
procedures in many different situations. These
devices are equipped with either a flame ionization (FID) or a photoionization
(PID) detector. The FID ionizes organic molecules via a hydrogen flame,
whereas the PID uses a lamp. Lamps
with different electron voltage (eV) may be used with the PID to ionize specific
groups or classes of organic compounds. For
specific lamp applications consult the owners manual.
These meters may be used for ambient air screening at sites for health
and/or safety reasons. They can be used for headspace analyses of soil samples to
determine "gross contamination" (17-770 F.A.C.), for well placement,
or for grid sampling. Calibration
and use of these types of meters should be performed
after
consulting the owners manual. There
are several procedures that must be accomplished at a minimum:
1. Calibration
must be performed on-site, prior to sampling, it is also suggested that
additional calibrations against one span gas be performed at 4 hour intervals
and/or at the end of the sampling day.
2. The meter must be
zeroed with "zero air" or equivalent.
If known to be free from interfering components, ambient air may be used.
3. At least one span gas
must be used for calibration.
4. Carbon filters must
be used to distinguish between methane and other aliphatic halocarbons (FIDs
only).
5. Background
corrections must be made if soil borings or split spoon samples are analyzed in
ambient air (unnecessary for headspace samples performed in mason jars under
foil).
6. Meters with PIDs must
be calibrated against a meter with a FID if headspace samples are being
performed for assessing "gross contamination" as defined in the Tanks
rule, Chapter 17-770, FAC.
7.5.8
Automatic Wastewater Samplers
These pieces of equipment are invaluable for remote sampling or for
sophisticated time- or flow-dependent sampling regimes.
Since loading calculations of industrial and domestic wastewater are
dependent upon the sampling accuracy, these devices must be volume calibrated by
checking the constant pumping volume at least twice with a graduated cylinder or
other calibrated container.
1. Instruments
must be initially calibrated each time the instrument is set up or upon failure
of any quality control calibration checks.
2. The number of
standards to be used for initial calibration must conform to method protocol or
general requirements in Section 7.6.3.
3. Correlation
coefficients for photometric analyses must be calculated and documented and
should be greater than or equal to 0.995.
4. A minimum of one
quality control check standard at a mid-range concentration shall be analyzed
prior to sample analyses to verify initial calibration.
This quality control check standard shall be prepared independently of
the calibration standards. Recoveries
for this check standard should be between 90 and 110%, or as specified by the
method.
1. One mid-range
continuing calibration standard must be analyzed for each group of 20 samples
analyzed. The check standard used
for initial calibration verification will verify acceptable calibration for the
first set of 20 samples.
Subsequent
sample sets of 20 or portions thereof (if a complete set of 20 is not
available), must have a continuing calibration check standard analyzed at the
beginning of each sample set.
2. Recovery
for the continuing calibration check standard shall be between 80 and 120%, the
range specified by the analytical method or the documented acceptance range that
is determined by internal historical data (see 9.2.3.4).
7.6.3
General Calibration Recommendations by Specific Analysis or Analysis
Type**
1. Titrimetric
Analyses - Standardize all titrants just prior to use.
2. Residue or Solids
Analyses
a.
Analyze Quality Control Check Samples on a quarterly basis.***
b.
See calibration requirements for analytical balances and ovens (Section
7.7.1 and 7.7.3).
3. Conductivity
a.
A minimum of 2 KCL standards must be analyzed bracketing the expected
concentration of the samples to be analyzed.
b.
The readings for the calibration standards must be within 1% of the
expected value.
c.
Continuing calibration checks must be within 1% of the true value.
4. Turbidity
a.
Calibration must be checked for each instrument testing range applicable
to the levels of turbidity to be measured.
b.
If formazin standards are not used for the daily calibrations, then
formazin standards must be prepared on a quarterly basis and compared with daily
standards.
c.
Calibration must be checked every 20 samples with 1 standard in each
applicable testing range.
d.
Acceptance criteria for all calibration and standard checks must be
established per instrument accuracy specifications.
5. Dissolved
Oxygen
a.
Probe - Calibrate against Winkler Titration on an annual basis.
Results should agree within 0.2 mg/l.
b.
Winkler Titration - see titration section (7.6.3.1).
6. Color and Chlorine
Final
determination made by comparison against Nessler Tubes or sealed color
standards.
a.
Confirm results against an approved alternate test procedure on a
quarterly basis.
b.
Results should be within 10% of the original value.
7. Temperature
a.
Laboratory thermometers must be checked against an NIST certified
thermometer on an annual basis. Results
must be within the manufacturer's specifications.
b.
Other devices used to record temperature must be checked on a monthly
basis against a thermometer that has been calibrated against an NIST certified
thermometer.
8. BOD
a.
Analyze a glucose/glutamic acid check sample each day BODs are analyzed.
b.
Check standard recovery must satisfy method criteria.
c.
See Dissolved Oxygen calibration protocols (7.5.4).
9. Oil and Grease
a.
See calibration criteria for the analytical balance (7.7.3).
b.
Analyze a QC check sample on a quarterly basis (all applicable matrices).
10.
Flash Point
a.
Analyze a solution of known flash point each day of operation.
b.
The flash point temperature should be within 5% of the literature flash
point value.
11.
Salinity
a.
Electrical Conductivity Method - follow protocols for conductivity
calibration and standardize instrument for seawater analyses according to method
protocol on a semiannual basis.
b.
Argentometric Method - standardize titrant daily and check method against
a known seawater sample or alternate method quarterly.
c.
Hydrometric Method - check method against the argentometric method or
with a QC check sample quarterly.
d.
Alternate method comparisons should agree within 10%.
12.
Chlorophyll - analyze a QC check sample quarterly (if available).
13.
Sulfate
a.
Gravimetric - analyze a QC check sample quarterly and follow calibration
requirements for the analytical balance (Section 7.7.3).
b.
Turbidimetric - see requirements for calibration of turbidity (Section
7.6.3.4).
c.
If sulfuric acid is used for standard preparation, then it must be
standardized with each preparation.
7.7
SUPPORT
EQUIPMENT CALIBRATION
1. Ovens
- temperature recorded daily. Temperatures
must be within acceptable method range.
2.
Incubators and water baths - monitor temperature twice daily for
microbiological work and once for other applications.
Temperatures must be within acceptable method ranges.
Must document that sterilization temperature
and pressure has been achieved by the use of sterilization indicators with every
autoclave run.
Monthly monitoring of Class S Weights.
Results must fall within the suppliers acceptance criteria.
Records must be maintained to document and verify acceptable instrument
or measuring system calibration for each analysis.
7.8.1
Records must be maintained for all standard preparations and working
standards must be easily traced to intermediate and primary standards used for
preparation.
7.8.2
Acceptable calibration verification (% recoveries, correlation
coefficients) must be recorded and easily identified with applicable daily
calibrations.
7.8.3
If calibration acceptance criteria are based on manufacturer's instrument
specifications or acceptable recoveries specified by QC check sample suppliers,
then records of such activities must be maintained.
Such records must be easily accessible and must establish verification of
acceptance criteria.
7.8.4
Laboratories must have available for inspection a table specifying
calibration acceptance criteria for all parameters.
7.9.1
Mid-Range Standard - a standard in the middle of the linear range
of the established calibration curve or a standard concentration in the middle
of the expected sample concentration range depending on the type of
determination to be performed.
7.9.2
Intermediate Standard - a standard prepared from the primary stock
standard which is diluted to prepare the working calibration standards.
7.9.3
Working Standards - the standards that are actually analyzed to
perform the instrument or measuring system calibration.
*
Acceptance criteria presented in this guidance document are general advisory
limits. Variances to the listed
criteria must be supported with documentation.
If the method stipulates different criteria, then the method criteria
must be used to verify acceptable calibration.
**
If analysis or analysis type is not mentioned in this SOP then method
calibration protocol and general requirements as presented in this guidance
document must be followed.
*** Recoveries for QC Check Samples should be between 90 and 110% or within acceptable ranges specified by the supplier